The Latest on Feeding Laminitic Horses

If your horse falls into the at-risk category, consider these diet changes

The basic principles of feeding laminitic horses are well-established: Avoid high-sugar and -starch feeds and lush green grass. However, recent research has given us even more insight into how to manage horses affected by or vulnerable to laminitis. First and foremost, we must identify at-risk horses and ponies, monitor them, and adjust how we manage them daily to help prevent this devastating hoof disease from developing.

Laminitis Risk Factors

Laminitis is an inflammatory disease of the leaflike laminae that suspend the coffin bone within the foot. In serious cases, the laminae can fail and separate from the coffin bone and the hoof wall, causing the bone to rotate or sink. Michelle Coleman, DVM, PhD, Dipl. ACVIM, of Texas A&M University’s (TAMU) College of Veterinary Medicine & Biomedical Sciences, in College Station, was the study coordinator for the American Association of Equine Practitioners (AAEP) Foundation’s Laminitis Research Working Group. In the group’s four-year case-control study, veterinarians looked at 199 cases of laminitis within four weeks of the onset of clinical signs. They compared these cases to 198 healthy horses and 153 horses that were Grade 3 to 5 lame in one forelimb with no history of laminitis. One hundred and nine veterinarians in 32 states and three Canadian provinces supplied the data for these 550 cases. “What we found is obesity was one of the biggest risk factors,” says Coleman, who is an assistant professor of large animal internal medicine at TAMU. “Reducing the risk of obesity may be important in reducing the risk of laminitis.” The study results showed that horses with a body condition score (BCS) of 7 or higher on the 1-9 Henneke scale or with generalized or regional adiposity (fat distribution all over or in certain areas) are at a greater risk of developing pasture- and endocrinopathy-associated laminitis (PEAL). The team found the following factors also increased a horse’s laminitis risk: 

  • High body morphometrics, such as the body condition score and generalized and regional adiposity, already mentioned, along with larger neck circumference and decreased height (as in a pony);
  • Recent diet or stabling changes;
  • Exposure to lush pasture;
  • Endocrine disease, such as pituitary pars intermedia dysfunction (PPID, or equine Cushing’s disease) and equine metabolic syndrome (EMS); and
  • Glucocorticoid administration, such as dexamethasone or prednisolone, within 30 days of the onset of clinical signs of laminitis. (Coleman cautioned that researchers need more supportive evidence of this potential—only 6% of horses met the criteria.)

“That study gives us further evidence that the hormonal situation of the horse is important to consider in terms of laminitis risk,” says Nicholas Frank, DVM, PhD, Dipl. ACVIM, professor of large animal internal medicine at Tufts ­University’s Cummings School of Veterinary Medicine, in Grafton, Massachusetts.

Veterinarians already know there’s a connection between obesity and insulin resistance and EMS in many laminitic cases. Normally, the pancreas produces the hormone insulin when glucose enters the bloodstream after a meal so cells can store and use glucose as an energy source and for metabolic processes in the body. Insulin resistance occurs when the body’s cells become resistant to glucose uptake, and the pancreas produces more and more insulin to try to keep blood glucose concentrations within normal limits. Excess insulin in the bloodstream is called hyperinsulinemia. Insulin resistance and hyperinsulinemia both fall under the umbrella of insulin dysregulation. It’s important to remember that not all insulin-resistant horses are obese and not all obese animals are insulin-resistant, but these two often go hand in hand.

Insulin dysregulation is one component of EMS, which is similar to metabolic syndrome in humans. Other EMS clinical signs can include previous or current laminitis; obesity; abnormal reproductive cycles; and abnormal fat deposits on the neck, back, sheath, tailhead, and above the eyes or as lumps along the body. 

Frank recommends owners have their veterinarians perform wellness evaluations on horses in any of these at-risk categories at least yearly and/or when management changes occur. “These are dynamic states, and we need to recheck to make sure we know what the status of the horse is,” says Frank.

The evaluations should include an oral sugar test and testing for PPID in middle-aged and older horses using a blood plasma adrenocorticotropic hormone (ACTH) test or a thyrotropin-releasing hormone (TRH) stimulation test. These tests usually run $100-300, says Frank. 

“Many horses that experience high insulin concentrations can be very well-managed, and we really can control these problems,” says Frank. “It’s heartening to know that we can improve the situation for the horse through good management.”

Diet to the Rescue

Coleman says diet and exercise are the best ways horse owners can manage their horses’ weight to prevent laminitis. “In the laminitic horse, exercise may not be possible, and so an appropriate diet will be essential,” she adds.

She advises owners to feed their at-risk or laminitic horses according to the animals’ energy requirements and use without overfeeding. Most importantly, avoid diets high in nonstructural carbohydrates (NSCs) such as glucose, fructose, sucrose, lactose, and starch.

While many people recommend soaking hay and dumping the sugary water before feeding, the resulting reduction in water-soluble carbohydrate (WSC, composed of sugars and fructan) content varies, says Patricia Harris, MA, PhD, VetMB, Dipl. ECVCN, MRCVS, an equine nutritionist specialist who manages the equine research program for the WALTHAM Centre for Pet Nutrition, in Leicestershire, United Kingdom. Soaking can cause nutrient and even dry matter loss, which is important for laminitis-prone horses and/or those in a weight-loss program. It can also increase the hay’s bacterial load. Harris suggests buying low-WSC hay (as verified by hay analysis), have it analyzed by a laboratory again after soaking, and add a vitamin and mineral forage balancer to the diets of horses consuming it.

Frank also suggests owners offer a balanced vitamin/mineral supplement to those forage diets lacking nutrients. Some horses, such as those that are still able to exercise, need additional calories, but from sources other than starch or sugars. Frank suggests offering these calories via low-NSC complete feeds or fat sources.

As a fat source, “vegetable oil is better than corn oil,” says Frank. “If you wanted to increase omega-3s and look more toward a flaxseed oil or a fish oil, you certainly could.”

While more research needs to be done on the effects of omega-3s, in a 2013 study researchers at Colorado State University looked at supplementing with omega-3 fatty acids using a marine source and a flax source. In insulin-­resistant mares, insulin sensitivity increased most with the marine source and to a lesser extent with the flax source.

Researchers on another study out of the M.H. Gluck Equine Research Center at the University of Kentucky, presented at the 2017 Equine Endocrinology Group’s Summit, showed that supplementing 16 grams of an algal source of the omega-3 docosahexaenoic acid to horses with EMS for 46 days reduced inflammation and improved insulinemic responses.

Because of all these complexities, Frank recommends consulting a veterinarian or nutritionist about at-risk horses’ diets.

Pasture Problems

An abrupt change in a horse’s grass intake is another risk factor for developing laminitis. In a one-year study of Danish horses with and without laminitis, Harris and Nanna Luthersson, DVM, found that allowing a previously pasture-restricted horse to have free-choice grass, or moving the horse to a new or larger paddock, resulted in a 40.5-fold increase in likelihood of a new laminitis case. Horses on high-quality fields, such as those with dense, well-managed, fast-growing grass, were 19 times more likely to develop laminitis.

“This suggests that grass intake may either be the cause or the final triggering factor for many animals developing new laminitis,” wrote the authors. “However, it is not clear whether this may be due to disturbances to the gut microflora, insulin dynamics, or a combination of both or some other factors.”

Coleman, too, cautions owners about their horses’ grass consumption. “We can easily regulate what they get in the barn—the hay and the grain—but we sometimes forget how much grass a horse can actually get when turned out,” she says, adding that grass has a higher NSC content in spring, late summer, and early fall.

Tips for Preventing Laminitis

When it comes to preventing laminitis, Harris says owners should be particularly careful when changing forage (fresh or preserved) types. “You may need several weeks to make the changeover,” she says.

Harris advises owners not to allow breeds prone to laminitis to graze without restriction, especially on high-quality pasture; some of these animals should not graze at all. Under such circumstances she recommends owners replace pasture with hay containing less than 10% WSC on a dry matter basis or use a suitable forage replacer to control calories and WSC intake while allowing horses to maintain their natural browsing (forage ingestion) behavior.

For gut health and welfare reasons, she says owners should offer forage at no less than 1.5% of the horse’s body weight per day on a dry matter basis, unless a veterinarian is monitoring the horse on a weight ­restriction program.

Frank says he rarely recommends keeping a horse in a stall because the isolation causes stress, which can raise insulin concentrations. Instead he recommends turnout in a small enclosure—­preferably a drylot—with another horse for social interaction. If a grass-free paddock isn’t available, Coleman recommends reaching for a grazing muzzle.

Harris, Annette Longland, PhD, DIC, and other British researchers have studied the benefits of a well-fitted grazing muzzle as part of a weight management program. They found that WSC intake decreased significantly in muzzled vs. unmuzzled ponies during a three-hour turnout.

They also found that muzzled ponies’ dry matter intake decreased by 77% in spring and summer and by 83% in autumn from their unmuzzled intake.

The Latest on Feeding Laminitic Horses

Along with diet, Coleman emphasizes the importance of exercise, if possible, for reducing at-risk horses’ weight. She cites a 2016 study in which de Laat et al. evaluated eight mixed-breed obese adult ponies using a dynamic feeding system with sliding doors that allowed ponies access to ­forage from only one side. When one door shut, they had to walk around a fence to the other side of the feeder to continue eating. On average, they traveled 3.7 times farther daily than when fed from a stationary feeder. This low-intensity exercise reduced the ponies’ body condition and cresty neck scores, along with body fat. It improved insulin sensitivity in those ponies using the dynamic feeder consistently and traveling more than 1.8 miles per day.

Lastly, Harris suggests monitoring affected and at-risk horses’ body condition scores regularly. “Make appropriate management changes if they are gaining (or losing) weight,” she says. “Being overconditioned (heavier) increases the risk of laminitis, but this does not mean that lean or moderate-conditioned animals (cannot) or will not get laminitis.”

Future Research

Both Frank and Coleman are interested in investigating the intestinal tract’s role in laminitis risk. “Are there changes in the microbial population within the intestinal tract that play a role in the development of laminitis and even in the exacerbation of hyperinsulinemia?” Frank says, adding that initial results from research in progress have shown some microbial differences between horses with EMS and those without.

Frank says he is optimistic about what future research will reveal about how to better manage at-risk and affected horses. “The consequences of mistakes in management are really quite high for laminitis-prone horses,” he says. “I think increased vigilance and increased awareness of how susceptible the animal is to laminitis is an important part of managing them.”